Downhole steam generation system and method

ABSTRACT

The present invention relates generally to a device, system and method for generating steam downhole. More particularly, the present invention relates to an electrical steam generation system that enables efficient production of downhole steam without the heat and pressure losses realized by surface steam generation equipment.

FIELD OF THE INVENTION

The present invention relates generally to a device, system and methodfor generating steam downhole. More particularly, the present inventionrelates to an electrical steam generation system that enables efficientproduction of downhole steam without the heat and pressure lossesrealized by surface steam generation equipment.

BACKGROUND OF THE INVENTION

In heavy oil recovery, the use of steam to assist in oil recovery iswell known. For example, it is common to drill parallel horizontal wellsinto formations at different levels containing heavy oil or bitumen.Such wells have been used in both Steam Assisted Gravity Drainage (SAGD)and Vapor-Extraction (VAPEX) production methods. In the SAGD system,steam is applied to an upper (or injection) well to contact heavyhydrocarbons inherent within the pores of the formation to decrease theviscosity of the hydrocarbons. In the VAPEX system, heated solvents areapplied. The steam or solvent increases temperature and pressure withinthe formation to reduce hydrocarbon viscosity which results inhydrocarbons collecting in a lower production (or recovery) well.

The current methods of injecting steam downhole are energy and capitalintensive. Steam plants on the surface produce steam in boilers usuallyutilizing natural gas or other fossil fuels as a combustible fuel. Thecapital costs associated with designing, building and operating asurface steam plant are significant requiring years of production fromthe formation to make the infrastructure investment worthwhile. As aresult, heavy oil recovery using surface steam production is generallyonly utilized for large scale projects with the result that smallerscale projects that could benefit from steam injection to aidhydrocarbon recovery are not utilized.

In addition, delivering high pressure steam to the formation isinefficient as the steam must be transported under pressure throughlengthy surface and well pipes to the formation. As the horizontal andvertical distances in a typical wellbore can be many thousands of feet,significant losses in steam pressure and temperature result therebyreducing the efficiency of the process.

As a result, there has been a need for steam production facilities withlower infrastructure costs that can deliver steam more efficiently todownhole formations.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a method of creatingin situ steam in a well for hydrocarbon recovery comprising the stepsof: positioning a downhole electrical steam generating system in thewell adjacent a hydrocarbon bearing formation; continuously formingdownhole steam within the well from in situ water; and, maintaining ahigh intra-well pressure to promote hydrocarbon recovery. In a preferredembodiment, the electrical steam generating system is conveyed to thehydrocarbon bearing formation by coiled tubing.

In further embodiments, high intra-well pressure is maintained by addingwater to the injection well from the surface or is maintained by asealed wellhead. In other embodiments, steam is generated in aninjection well and hydrocarbons are recovered from a recovery well orsteam is generated in the well and hydrocarbons are simultaneouslyrecovered from the well. Still further, the system may include at leasttwo generation systems are operatively connected together to enablesteam generation at separate locations within the well.

In accordance with another embodiment, a downhole steam generationsystem for hydrocarbon recovery is provided comprising: a housing havingopenings operatively containing an electrical immersion heater, aconnector system for connecting the electrical immersion heater to anelectrical cable, and, a surface power unit for delivering electricalpower to the electrical heater through the electrical cable.

The electrical immersion heater preferably includes a thermocoupleoperatively connected to the surface power unit for controlling thesurface temperature of the immersion heater.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described withreference to the attached Figures, wherein:

FIG. 1 is a schematic diagram showing a typical deployment of a steamgeneration system in accordance with one embodiment of the invention;

FIG. 2 is an isometric view of a steam generation system in accordancewith one embodiment of the invention;

FIG. 3 is a side view of a steam generation system in accordance withone embodiment of the invention;

FIG. 3A is a cross-sectional view of a steam generation system inaccordance with one embodiment of the invention;

FIG. 3B is a cross-sectional view of a connector system of a steamgeneration system in accordance with one embodiment of the invention;

FIG. 3C is a cross-sectional view of a downhole end of a steamgeneration system in accordance with one embodiment of the invention;

FIG. 4 is a schematic diagram of the deployment of a steam generationsystem in accordance with a further embodiment of the invention;

FIG. 4A is schematic cross-sectional view of a connector system at adownhole end of a steam generation system in accordance with oneembodiment of the invention; and

FIG. 4B is schematic cross-sectional view of a connector system at anuphole end of a steam generation system in accordance with oneembodiment of the invention.

DETAILED DESCRIPTION

Generally, the present invention provides a device, system and methodfor electrically producing steam downhole.

With reference to the Figures, a downhole steam generation system andmethods of deployment are described. The system includes a downholeheating device 10, conductors 12 and a surface control unit 14. As shownin FIGS. 2, 3, 3A, 3B, 3C and 3D, the downhole heating device 10generally includes a housing 10 a with openings 10 b encasing animmersion heating element (IHE) 10 c and a conductor connection system10 d.

Downhole Heating Device 10

Housing 10 a

The housing 10 of the downhole heating device is a hollow cylindricalelement with openings 10 b designed to allow the passage of fluids intothe housing and to contact the IHE where the production of steam occurs.The openings 10 b are generally of a fixed dimension having sizes andpositions designed a) to allow sufficient fluids to enter the housing,b) to provide structural integrity to the housing and c) to protect theimmersion IHE downhole. In a preferred embodiment, the housing isconstructed of 100% stainless steel and is preferably the same materialas the outer surfaces of the IHE so as reduce the risk of deteriorationby dissimilar metal and/or galvanic corrosion. Appropriate grades ofstainless steel can be used to comply with industry standards enablinguse of the system in both sweet and sour gas wells. The housing isadapted for attachment to coiled tubing by any suitable means known tothose skilled in the art including specialized connectors and lockingsystems. In a preferred embodiment, the housing includes a bullnose end10 e that facilitates pushing the downhole heating device to a desiredlocation (discussed below).

Immersion Heating Element 10 c

The IHE 10 c is an electric resistance heating element designed tooperate between ambient temperatures and a maximum temperature, themaximum temperature being approximately 1400° F. Generally, it ispreferred that the maximum temperature can be achieved within a fewseconds of applying power to the IHE through power supplied through theconductor 12 and surface control unit 14. The IHE is thermaticallycontrolled by an integral thermocouple (not shown) that communicateswith the surface control unit 14. Preferably, under normal operatingconditions, in order to maximize the operating life of the IHE and toprevent hydrocarbon cracking, the IHE is operated at temperatures in therange of 400-500° F.

The IHE is preferably powered by a 480 volt alternating current, singlephase power source delivering 12,000 Watts or approximately 300 Wattsper square inch of IHE surface area. In a typical embodiment, the IHEwill be approximately 20-40 inches in length and have an outsidediameter of approximately 0.6 inches.

In various embodiments of the downhole heating element, additionalfunctionality may be incorporated within the IHE such as fluid detectionsensors and/or pressure sensors. Over temperature protection may also beprovided.

The resistance heating element is encased within an IHE housing toprotect the resistance heating element. The construction is also sealedto prevent contact of fluids with the resistance heating element.

The IHE is mounted within the housing by any suitable means. As shown inFIG. 3A and FIG. 3B, the IHE is secured to a mounting wall 10 f by abushing 10 g.

Connectors 10 d

As shown in FIGS. 3A and 3B, the system includes connectors that ensurea robust electrical connection between the IHE and conductors for theoperating temperatures and downhole conditions. In addition, theconnectors must also provide sufficient mechanical strength in tension,compression and torsion for the operating conditions. As shown, theconnectors include a pin connector 10 d over which a correspondingfemale connector (not shown) may be placed. To ensure longevity inoperation, the IHE and connectors may also be welded into place.

Conductors 12

Power is delivered to the IHE through conductors 12. The conductors aredesigned to deliver power over at least 2500 feet to the IHE whileenabling the surface controller to maintain an IHE surface temperature±1° F. The conductors must provide sufficient mechanical strength tosupport the weight of the conductors over these distances and haveappropriate coverings to provide the appropriate abrasion resistance.

Surface Control Unit and Power Supply 14

As described above, the surface control unit 14 controls the delivery ofpower to the IHE through the conductors. Power may be delivered throughmains or on-site generated power. In a generator application, thegenerator is preferably truck 8 or trailer mounted allowing readydelivery of the surface control unit 14 to the well-site. Known dieselgenerators may be used and should be capable of delivering single andthree phase power to within 1% of the desired voltage. A suitable truck-or trailer-mounted genset for a 45 kVA/36 kW generator deliveringroughly 12,000 Watts to the IHE will consume roughly 6 liters of dieselfuel per hour.

The surface control unit 14 allows the control and delivery of power tothe IHE. The SCU will preferably include appropriate displays andswitches to enable an operator both to set and monitor power levels.

Operation

In operation, the downhole heating device is configured to a coiledtubing 12 a system with the conductor 12 carried within the coiledtubing in order to protect the conductor and to allow the downholeheating device to be pushed to a desired location within a wellbore 20.The surface control unit 14 may be mounted on a truck or trailer fordelivery to the well site. After delivery to the well site, theappropriate connections between the coiled tubing, conductor, downholeheating device and surface control unit are made.

Once attached to the coiled tubing, the downhole heating device isconveyed to the desired location. In various formations, the formationmay provide sufficient in situ water to generate the desiredtemperatures and pressures of steam within the formation for hydrocarbonrecovery. Alternatively, additional water may be added to the annularspace 20 a between the wellbore 20 and coiled tubing 12 a. Downholepressure may be maintained either by hydrostatic pressure above theheating device 10 or by appropriate wellhead systems as is known in theart.

The methodology is similarly effective in solvent flood methods wherehydrocarbon solvents are added to the well.

Heating losses and hence the cost of downhole heating is reducedsignificantly over past techniques which lead to significantimprovements in sweep efficiency.

In addition to heavy oil recovery, the system may also be used in thestimulation of conventional vertical wells through alternating steam andproduction steps, often referred to as “huff and puff”. In thismethodology, the downhole heating device is conveyed to the stimulationzone and the formation is stimulated. The downhole heating device may beremoved from the well and standard production of the well may follow. Ina still further embodiment, specialized well heads may be utilizedallowing both pumping equipment and the downhole heating device to bepositioned in the same well thereby obviating the need to remove thedownhole heating device before production.

Series Operation

In further embodiments of the invention, it may be desired to providestimulation in horizontally or vertically separated zones of the samewell bore 20. As shown in FIG. 4, separate downhole heating devices 10′and 10″ are shown separated by a section of coiled tubing within a wellbore 20. Downhole heating device 10′ may be a downhole heating device asdescribed above whereas 10″ is a distinct assembly. In particular,embodiment 10″ is distinct from embodiment 10′ to allow conductors topass across or through the housing, through coiled tubing section 11 todownhole heating device 10″. As shown, the uphole ends of 10′ and 10″are similar whereas the downhole end of 10′ is provided with a bull nose10 e. The downhole end of 10″ may include a connector system similar tothat described above. The housing of 10″ is distinct in allowingconductors to pass along or through the housing to the connectors. Asshown in FIGS. 4A and 4B, coiled tubing 11 may be attached to housing 10a. In FIG. 4A, the conductors 12 are attached to a connector 10 d asdescribed above. Within connector 10 d, the conductors are split and arepassed through appropriate openings 10 h and along channels 101.Channels 10 i may be covered by coverings 10 j. At the opposite end ofthe housing, conductors pass through further openings to a downholeconnector 13 which allow a further conductor 12′ and tubing section 11′to connect to 10″ thus permitting 10′ to be connected in series with10″.

The above-described embodiments of the present invention are intended tobe examples only. Alterations, modifications and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

1. A method of creating in situ steam in a well for hydrocarbon recoverycomprising the steps of: positioning a downhole electrical steamgenerating system in the well adjacent a hydrocarbon bearing formation;continuously forming downhole steam within the well from in situ water;and, maintaining a high intra-well pressure to promote hydrocarbonrecovery.
 2. A method as in claim 1 wherein the electrical steamgenerating system is conveyed to the hydrocarbon bearing formation bycoiled tubing.
 3. A method as in claim 1 wherein the high intra-wellpressure is maintained by adding water to the injection well from thesurface.
 4. A method as in claim 1 wherein the high intra-bore pressureis maintained by a sealed wellhead.
 5. A method as in claim 1 whereinsteam is generated in an injection well and hydrocarbons are recoveredfrom a recovery well.
 6. A method as in claim 1 wherein steam isgenerated in the well and hydrocarbons are simultaneously recovered fromthe well.
 7. A method as in claim 1 wherein at least two generationsystems are operatively connected together to enable steam generation atseparate locations within the well.
 8. A downhole steam generationsystem for hydrocarbon recovery comprising: a housing having openingsoperatively containing an electrical immersion heater, a connectorsystem for connecting the electrical immersion heater to an electricalcable, and, a surface power unit for delivering electrical power to theelectrical heater through the electrical cable.
 9. A downhole steamgeneration system as in claim 8 wherein the housing is adapted foroperative connection to coiled tubing.
 10. A downhole steam generationsystem as in claim 9 wherein the electrical cable is contained withinthe coiled tubing.
 11. A downhole steam generation system as in claim 10wherein the electrical immersion heater includes a thermocoupleoperatively connected to the surface power unit for controlling thesurface temperature of the immersion heater.
 12. A downhole steamgeneration system as in claim 8 wherein the housing and connector systemenable two or more downhole steam generation systems to be operativelyconnected together across one or more sections of coiled tubing toenable simultaneous steam production at one or more locations within thewell.